1. Field of the Invention
This invention relates to compositions of matter useful in performing extracapsular cataract operations and to a method of performing such operations with the use of such compositions. More particularly, the invention relates to the use of a solution of alpha-chymotrypsin in the area of operative treatment of grey cataract.
2. Description of the Prior Art
Grey cataract is an ailment of the eye in which there develops a darkening or clouding of the lens and a decrease of vision produced thereby. By a so-called intracapsular operation, the darkened or clouded lens, which is located in a capsule, is removed by extraction as a whole together with the capsule.
By another method, a so-called extracapsular operation, which is presently widely used, the darkened or clouded lens is likewise removed, but the posterior capsule is left behind. In performing an extracapsular operation, the anterior capsule of the lens is removed and then the main part of the lens and the intracapsular posterior rind coating are drawn away with the aid of a flushing process with simultaneous irrigation. There also exists the possibility of using an ultrasonic sound apparatus for the destruction of the main body of the lens and its removal by aspiration. In most cases, there is practiced in such operations the subsequent implantation of a clear typically glass-bodied posterior chamber lens which replaces the removed darkened or clouded lens. A prerequisite for this is that the posterior capsule be exposed by the operation and that the capsule be completely clear so that optimum physiological (optical) properties including complete light transmission are restored, hence indicating success of the operation. It is known to mechanically polish the posterior capsule before the implantation of the posterior chamber lens. However, despite careful polishing, there frequently develops a so-called capsule fibrosity; this concerns a thickening of the capsule because of very fine particles which cannot be seen microscopically but which form a thickened film on the capsule during the operation.
Alpha-chymotrypsin is a substance that in its cleanest, crystallized, dialyzed and stabilized form is commercially available. Its molecular weight is 22,500; its isoelectric point lies between a pH value of 5 to 4, with the effective maximum being at 8.1 to 8.6.
The use of alpha-chymotrypsin is known for the practice of intracapsular operations. In such operations, it is used in a dilution of 1:5,000 to about 1:10,000 and it serves for enzymatic zonulolysis, that is, the dissolution of the zonule fibers that hold the lens in tension. It was therefore surprising to establish, and not foreseeable, that the same substance could be used in a dilution of 1:10,000 to 1:30,000 whereby the fibers are not dissolved and the solution can be used for the cleaning of the posterior capsule.
During such cleaning, it has been discovered that, in some circumstances, there exists a problem in that liquid present in the eye or liquid forming or collecting in the capsule may undesirably further dilute the alpha-chymotrypsin solution. Accordingly, there has been a need for a further modification or improvement in accordance with which the composition of the alpha-chymotrypsin solution is suitably modified to overcome this problem. There is a looseleaf reference work, periodically updated and available to U.S. pharmacists, called "Facts and Comparisons", published by the Lippincott firm of St. Louis, Missouri, and it contains information that sodium hyaluronate is known to be naturally present in the aqueous humour and vitreous humour of the eye, and that sodium hyaluronate is known as a specific material which is useful in extracapsular eye surgery. There is not to be derived from this information, however, any particular suggestion of its role in the preferred embodiment of the present invention.